903
FXUS65 KBOI 260337
AFDBOI
AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE BOISE ID
837 PM MST THU DEC 25 2025
DISCUSSION
THUNDERSTORMS DEVELOPED LATE TODAY AND EARLY
EVENING IN IDAHO BETWEEN EMMETT AND MCCALL. FRIDAY WILL BE THE
LAST DAY OF SPRING-LIKE WEATHER IN OUR CWA BEFORE A COLD FRONT
AND UPPER TROUGH COME IN FROM THE NORTH. THE COLD FRONT, DUE
FRIDAY NIGHT, AND POST-FRONTAL WINDS SATURDAY HAVE BOTH TRENDED
STRONGER IN LATEST MODELS WHICH INTENSIFY THE ASSOCIATED UPPER
TROUGH AS IT DIGS SSE-WARD FROM BC. WE MAY NEED TO UPGRADE OUR
EXISTING WINTER WEATHER ADVISORY TO WINTER STORM WARNING FOR THE
IDAHO MOUNTAINS NORTH OF THE SNAKE BASIN, ESPECIALLY DURING AND
AFTER THE COLD-FRONTAL PASSAGE. RISING AIR AHEAD OF THE FRONT,
AND FORCED LIFT BY ASCENT OVER HIGHER TERRAIN, WILL ENHANCE
SNOWFALL, AND RAPIDLY FALLING TEMPERATURES BEHIND THE FRONT WILL
CAUSE ROADS IN THE MOUNTAINS TO BECOME ICY AND SNOW-COVERED,
WHILE GUSTY WINDS CREATE BLOWING AND DRIFTING OF SNOW AND
REDUCED VISIBILITY. CURRENTLY FORECAST SNOW AMOUNTS ARE BELOW
WARNING CRITERIA, BUT TOGETHER WITH THE EXPECTED BLOWING AND
DRIFTING AND DETERIORATING ROAD CONDITIONS AN UPGRADE TO
WARNING WOULD BE JUSTIFIED. TO THE SOUTH, AS THE COLD FRONT
MOVES ACROSS THE SNAKE BASIN PRE-DAWN SATURDAY, RAIN WILL LIKELY
CHANGE TO WET SNOW AND MAY ACCUMULATE SLIGHTLY BEFORE ENDING,
ALTHOUGH ROADS WILL STAY WET. HOWEVER, POST-FRONTAL WEST WINDS
WILL INCREASE TO 20 TO 30 MPH WITH GUSTS 40 TO 50 MPH LATER
SATURDAY, STRONG ENOUGH FOR A WIND ADVISORY. WILL LET THE MID
CREW MAKE THE CHANGES AFTER ALL THE NEW MODEL DATA HAVE COME IN.
IN ANY CASE, GET READY FOR A SHARP CHANGE TO WINTRY WEATHER
FRIDAY NIGHT THROUGH SATURDAY.
AVIATION
SCATTERED SHOWERS OVERNIGHT INTO FRIDAY AFTERNOON,
INCREASING COVERAGE FRI NIGHT. ISOLATED LIGHTNING. MVFR-LIFR
CONDITIONS IN PRECIP/LOW CLOUDS. BLOWING SNOW IN MTNS FRI. SNOW
LEVELS: 4.5K-6.5K FT MSL OVERNIGHT, LOWERING TO 3.5K-4.5K FT MSL
BY MID-DAY FRI. MTNS OBSCURED. POTENTIAL FOR LLWS FRI AM. SURFACE
WINDS: E TO S 5-15 KT, INCREASING FRI MORNING TO SW-S 15-25 KT
WITH 25-45 KT GUSTS. WINDS ALOFT AT 10KFT MSL: SW 35-55 KT.
KBOI...VFR. INTERMITTENT RAIN SHOWERS THROUGH MID-MORNING FRI,
THEN DRY. POTENTIAL FOR LOW-LEVEL WIND SHEAR OVERNIGHT. SURFACE
WINDS: SE- SW 5-15 KT. OCCASIONAL GUSTS TO 20-25 KT THROUGH FRI
AFTERNOON.
WEEKEND OUTLOOK...SNOW LEVELS LOWERING TO VALLEY FLOORS
SATURDAY. SCATTERED TO NUMEROUS SNOW SHOWERS SATURDAY, WITH
MVFR-LIFR CONDITIONS IN PRECIP. MTNS OBSCURED. SHOWERS ENDING
SATURDAY EVENING. VFR, COLD, DRY SUNDAY. SURFACE WINDS: W TO
NW 15-25 KT SATURDAY WITH 25-35 KT GUSTS. LIGHT WINDS SUNDAY.
AIR STAGNATION
HIGH PRESSURE IS FORECAST TO BUILD OVER THE
REGION BEGINNING SATURDAY NIGHT AND WILL STRENGTHEN THROUGH THE
EARLY PART OF NEXT WEEK. THIS PATTERN WILL FAVOR THE DEVELOPMENT
OF A STRONG AND PERSISTENT SURFACE-BASED TEMPERATURE INVERSION
FROM SUNDAY THROUGH AT LEAST NEXT TUESDAY. WITH LIGHT WINDS AND
LOW MIXING HEIGHTS (1000-2000 FEET) EXPECTED UNDER THE RIDGE,
THERE IS INCREASING CONCERN FOR DETERIORATING AIR QUALITY AND
POOR VENTILATION IN THE SHELTERED VALLEYS OF SOUTHEAST OREGON
AND SOUTHWEST IDAHO. WHILE IT MAY BE TOO EARLY FOR A FORMAL
ADVISORY, CONDITIONS WILL BE MONITORED CLOSELY AS THE STAGNANT
AIR MASS BECOMES ESTABLISHED.
PREV DISCUSSION
SHORT TERM...TONIGHT THROUGH SATURDAY NIGHT...THE TEMPERATURE,
AS OF WRITING THIS, HAS REACHED 58 DEGREES IN BOISE. THIS PUTS
THIS CHRISTMAS AS THE SECOND WARMEST ON RECORD. SHOWER COVERAGE
WILL INCREASE THROUGHOUT THE AFTERNOON AS AN UPPER-LEVEL JET
CONTINUES TO OVERSPREAD ACROSS OUR AREA. WITH INCREASING
DYNAMICS, MOISTURE, INSTABILITY, AND STEEPENING LAPSE RATES,
ADDITIONAL SHOWERS WILL TAKE ON MORE OF A CONVECTIVE NATURE.
LIGHTNING FLASHES HAVE ALREADY BEEN OBSERVED IN EASTERN IDAHO
AND NORTHERN NEVADA. CURRENT MESOSCALE ANALYSIS HAS SHEAR VALUES
OF 45-55 KTS OVER OUR AREA. THESE VALUES WILL CONTINUE TO INCREASE
AS THE JET MAX MOVES OVER. WHILE THIS STRONG SHEAR MAY WORK TO
TEAR APART UPDRAFTS THAT TRY DEVELOPING WITH WEAK CAPE, LOCALLY
HEAVIER PRECIP, GUSTY WINDS, AND LIGHTNING WILL BE IN PLAY WITH
THE STRONGEST SHOWERS. THIS THREAT WILL STICK AROUND IN THE
WEST CENTRAL/IDAHO MOUNTAIN ZONES THROUGH FRIDAY MORNING.
PRECIPITATION WILL CONTINUE COME FRIDAY, AS THE MAIN UPPER
LEVEL TROUGH AND SURFACE COLD FRONT MOVE ACROSS THE AREA. THIS
FRONT WILL LOWER DAYTIME HIGH TEMPERATURES BY 5-10 DEGREES.
SNOW LEVELS WILL ALSO DROP TO 3.5-5 KFT MSL BY FRIDAY AFTERNOON.
HAVE EXPANDED THE WINTER WEATHER ADVISORY TO INCLUDE THE BOISE
MOUNTAIN ZONE IN COLLABORATION WITH NEIGHBORING OFFICES. HIGHER
ELEVATION MOUNTAIN VALLEYS WILL SEE 4-7 INCHES OF SNOWFALL
FRIDAY THROUGH SATURDAY MORNING, WITH UP TO 19 INCHES AT BANNER
SUMMIT.
SNOW LEVELS WILL DROP TO VALLEY FLOORS BY SATURDAY AFTERNOON;
ALTHOUGH WITH DECREASING UPPER-LEVEL SUPPORT AS THE TROUGH MOVES
EAST, PRECIPITATION CHANCES WILL BE ON THE DECLINE THROUGHOUT
THE DAY SATURDAY. ANY ADDITIONAL PRECIPITATION IN LOWER
ELEVATIONS WILL BE SNOW OR WINTRY MIX. HOWEVER, NO ACCUMULATION
IS EXPECTED. ADDITIONAL SNOW ACCUMULATIONS IN THE MOUNTAINS
WILL BE LIMITED TO UP TO 1.5 INCHES. COME SATURDAY NIGHT,
PRECIPITATION CHANCES WILL TAPER OFF ENTIRELY AS RIDGING BEGINS
TO BUILD IN. THIS WILL MAKE WAY FOR A MORE STAGNANT, STABLE
PATTERN IN THE LONG TERM PERIOD.
LONG TERM...SUNDAY THROUGH THURSDAY...A BROAD RIDGE OF HIGH
PRESSURE WILL BUILD OVER THE WESTERN US ON SUNDAY, BRINGING
AIR STAGNATION CONCERNS AND DRY CONDITIONS THROUGH THE MIDDLE
OF NEXT WEEK. COLD POOLS AND PATCHY FOG WITH LOW STRATUS
CLOUDS WILL LIKELY DEVELOP IN THE VALLEYS DUE TO LIMITED
DAYTIME MIXING, WITH ABOVE NORMAL TEMPERATURES MIDSLOPE AND
ON RIDGETOPS. MODEL AGREEMENT REMAINS CONSISTENT ON THE
DEVELOPMENT OF THE RIDGE AND THE DRY PATTERN FOR EARLY NEXT
WEEK, WITH SOME DISCREPANCIES IN THE PATH OF A TROUGH BY THE
END OF THE LONG TERM PERIOD (THURSDAY). SOME MEMBERS ARE
DIGGING THE TROUGH INTO THE REGION, BRINGING COLD AIR AND THE
POTENTIAL FOR SNOW ON VALLEY FLOORS, WHILE OTHERS KEEP THE
COLDEST AIR TO OUR NORTH AND WEST, KEEPING US IN WARM SOUTHWEST
FLOW WHICH WOULD KEEP SNOW LEVELS HIGHER (AROUND 5000-6000 FEET
MSL). AT THIS POINT, AGREEMENT EXISTS ON THE PATTERN SHIFT BACK
TO WET WEATHER, BUT THE TRACK OF THE COLDEST AIR REMAINS
UNCERTAIN. THE CLIMATE PREDICTION CENTER 6-10 DAY OUTLOOK FAVORS
ABOVE-NORMAL TEMPERATURES CONTINUING (60% CHANCE) WITH ABOVE-
NORMAL PRECIPITATION.
BOI WATCHES/WARNINGS/ADVISORIES
ID...WINTER WEATHER ADVISORY FROM 5 AM FRIDAY TO 5 AM MST SATURDAY
IDZ011-013.
OR...NONE.
WWW.WEATHER.GOV/BOISE
INTERACT WITH US VIA SOCIAL MEDIA:
WWW.FACEBOOK.COM/NWSBOISE
WWW.X.COM/NWSBOISE
DISCUSSION...LC
AVIATION.....SH
AIR STAGNATION...JDS
SHORT TERM...NF
LONG TERM....SA
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